A comparison of impression partial dentures
materials
Georgia S. Dounis, D.D.S.,* Gerald J. Ziebert, Kiki S. Dounis, D.D.S.*
for complete-arch
fixed
D.D.S., M.S.,** and
Marquette University, School of Dentistry, Milwaukee, Wis. This study compared the marginal fit of complete-arch fixed prostheses under simulated clinical conditions. Prostheses were made on casts constructed from three commonly used impression materials; polyether, polyvinyl siloxane (mediumviscosity and putty-wash), and reversible hydrocolloid. A maxillary dentoform with four abutment teeth was used as the master cast and six impressions were made with each material. Individual castings for each abutment were made on the stone casts. The abutment castings were luted together on the casts to provide a complete-arch fixed partial denture using a ticonium framework and acrylic resin. The marginal fit of the abutment castings was measured on the master cast before and after the prostheses were luted together. The polyether and both addition silicone impression materials were significantly more accurate than the reversible hydrocolloid in both situations. All of the single castings were clinically acceptable, but the luted restorations made from reversible hydrocolloids were not. (J PROSTHET DENT 1991;65:165-9.)
D.
lmensional accuracy of impression materials is crucial for the production of working casts in fixed prosthodontics. Accurate replications of tooth preparations
and their arch positions require impression materials that exhibit limited distortion. Research on dimensional
stability
of impression
materi-
als commonly has concentrated on the accuracy of individual dies1-6 and quadrant fixed partial denture (FPD) abutments.7-12 Few studies have reported the accuracy of complete-arch
impressions.
Henry
and Harnist13
com-
pared the accuracy of 14 different impression materials by using a four-posted, silver-plated, full-arch model. They concluded that polyethers were the most reliable. A study of full-arch impressions of two machined aluminum alloy dies14found addition-silicones the most stable, followed by polyethers. Another study,15 using a full-arch metal model, compared impression materials by measuring faciolingual and mesiodistal widths and the height of the stone casts versus the master model. Reversible hydrocolloid produced less interabutment distortion. The accuracy of six impression materials, used in complete-arch FPD impressions with four intricate abutment preparations machined of
stainless steel was investigated,16 and a similar study used complete crown preparations on a dentoform (Columbia Dentoform Corp., New York, N.Y.) model to compare the accuracy of six impression materials.‘? In both studies, a prosthesis was made on the master model and adaptation was evaluated on casts obtained from the various impression materials. Both concluded that polyethers, followed by addition silicones, produced the most accurate working casts. Neither reflected the procedure normally followed in restorative therapy. In clinical situations, restorations are made on working casts and then placed in the mouth. Our experiments used castings that were made and assembled on the working cast and then placed on the master model, to determine the accuracy of four commonly used impression materials. METHODS
AND
MATERIAL
Three impression materials were used in this study: polyether (Impregum F, Premier, ESPE, West Germany); addition silicone (Mirror 3 medium-viscosity, single-mix, and Mirror 3 putty-wash, Sybron/Kerr, Romulus, Mich.); and reversible hydrocolloid (Acculoid, Van R, Los Angeles, Calif.).
Presented at the Academy of Denture Prosthetics meeting, Corpus Christi, Tex. *Graduate student, Department of Prosthodontics. **Professor and Chairman, Department of Prosthodontics. 10/l/21771
THE
JOURNAL
OF
PROSTHETIC
DENTISTRY
Six satisfactory impressions were obtained for each of the materials for a total of 24 impressions. A maxillary partially edentulous model (Model No. 567M, Columbia Dentoform Corp.) was modified as the master model. The first premolars were removed and the sockets were filled with inlay pattern resin (Duralay, Reliance Dental Mfg. Co., Worth, Ill.). The remaining canines (teeth No. 6 and
165
DOUNIS,
ZIEBERT.
AND
DOUNIS
Fig. 1. Modified dentoform model with abutment preparations used as master model. Fig. 2. Ticonium framework used to lute FPD. Fig. 3. Measuring sites for each abutment. MB, Mesiobuccal measuring position; B, buccal measuring position; DB, distobuccal measuring position. Fig. 4. FPD luted together with ticonium framework by Duralay resin.
11) and second molars (teeth No. 2 and 15) were the four abutment teeth for the maxillary prosthesis. The root surfaces of the abutment teeth and their respective sockets were roughened and scored. The sockets were filled with DuraIay resin, the teeth were immediately replaced, and the screws were tightened to secure each abutment to the base. After 48 hours the abutment teeth were prepared for complete crowns with 1 mm shoulder margins by use of a handpiece mounted on a parallelometer (Fig. 1). A handle was mounted on the base of the dentoform to enhance separation of the impressions from the models in a straight line to minimize distortion. For the polyether and addition-silicone impressions, custom acrylic resin trays were constructed with a 4 mm uniform space. Metal rimlocked water-cooled trays were used for the reversible hydrocolloid impressions. An acrylic resin stop was placed in the palatal region of the rim-locked tray to provide a minimum of 2 mm of space over the occlusal surfaces of the abutments. The setting time for the polyether and addi-
166
tion-silicone materials was doubled to compensate for polymerization at room temperature. For the reversible hydrocolloid impressions, the dentoform was tempered at 98” F for 10 minutes before the impressions were made. The temperature of the water circulating through the tray had a range of 65’ to 72’ F and the impression was allowed to gel for 8 minutes. All of the impressions were manually held in place throughout the setting period. The impressions were immediately poured in a vacuum-mixed die stone (Die Keen, Columbus Dental Mfg., St. Louis, MO.), except the addition silicones, which were poured after 20 minutes. The casts of the reversible hydrocolloid impressions were placed in a humidor while setting. The casts were separated after 1 hour, trimmed after 2 hours, and examined under X10 magnification to remove minor bubbles with a sharp instrument. Individual ceramometal cast copings (Olympia, J. F. Jelenko & Co., Armonk, N.Y.) were made for each of the abutment dies on the 24 casts for a total of 96 castings. The flat occlusal surface of each coping was roughened to facil-
FEBRUARY
1991
VOLUME
65
NUMBER
2
IMPRESSION
MATERIALS
FOR
COMPLETE-ARCH
FPDs
I. Mean marginal openings of individual castings at each abutment (in pm)
Table
Table II. Mean marginal openings of assembled castings at each abutment (in km) Abutment
Abutment
Type of impression
Right second molar --f
Left second molar
Left canine
Right canine
SD
Ti
SD
si
SD
ii
SD
x
-
Right canine
SD
iI
Left canine
Left second molar
Tt
iii
-
SD
SD
SD
1
10
8
19
8
34
10
7
5
1
38
13
36
9
24
8
20
2
41
18
17
7
29
12
6
5
2
40
14
8
5
34
11
10
9
3
41
11
34
10
43
15
28
9
3
54
11
25
9
21
8
60
14
4
37
15
66
6
120
20
28
10
4
75
18
125
16
123
21
141
29
Materials: 1, Polyether; 2, vinyl polysiloxane (medium polysiloxane (putty/wash); 4, Reversible hydrocolloid.
viscosity);
3, vinyl
itate attachment of a cast ticonium framework used to lute the copings together (Fig. 2). The castings were examined under X10 magnification, small bubbles and irregularities were removed, and the copings were fitted to their respective dies. Each cast was mounted on a surveyor table. The individual castings were seated with light finger pressure and the vertical marginal discrepancy was measured with a travelling microscope graduated in 0.001 mm. Three sites were measured: the mesiofacial (MF), midfacial (F), and distofacial (DF) aspect of each casting for Nos. 2,6,11, and 15. The same measuring procedure was followed after the copings were placed on the Dentoform model (Fig. 3). The copings were returned to the stone casts and luted together by use of inlay resin (Duralay) and the ticonium framework (Fig. 4). The luting procedure was completed one joint at a time, with a lo-minute setting time allowed before proceeding to the next joint. The marginal openings were again measured at the three sites of each abutment. The one-piece unit was then removed from the stone dies, seated on the dentoform with light finger pressure, and the vertical marginal discrepancies were again measured at the designated sites.
RESULTS The mean marginal openings for all of the castings on the working casts were less than 0.025 mm. Table I shows the mean marginal opening of the individual castings at each abutment on the dentoform. Table II shows the mean marginal opening of the castings on the dentoform after they had been luted on the working cast and transferred to the dentoform. To assess the difference among the materials, a one-way analysis of variance was performed of material on the cast, on the dentoform, luted on the cast, and on the dentoform after the specimen was luted on the cast. The analysis of the unassembled castings on the dentoform revealed significant differences (p < 0.05) among the materials. The analysis also disclosed significant differ-
THE
-
Type of impression
Right second molar
JOURNAL
OF PROSTHETIC
DENTISTRY
Material: 1, Polyether; 2, vinyl polysiloxane (medium polysiloxane (putty/wash); 4, Reversible hydrocolloid.
Table
III.
viscosity);
8
3, vinyl
Summary of analyses of variance
Source of variation
DF
SS
3
MS
F-Ratio
p
14.0079
0.05). *Significant @ < 0.05).
DISCUSSION Consistent with previous reports,61iis 16*l7 this study demonstrated that polyether impressions were the most accurate. The addition silicones were a close second and not inferior when judged statistically. The reversible hydrocolloids were the least accurate of the four forms of materials, showing statistically significant differences from the rest. This difference held true whether the castings were fitted to the master model individually or luted to create a complete-arch restoration. With the range of clinically acceptable open margins as reported by Christensen18 (0.034 mm to 0.119 mm with a mean of 0.074 mm) and by Dedmonlg (mean of 0.114 mm), it is evident that the unassembled units made from all four forms of impression materials would be clinically acceptable. Mean vertical marginal discrepancies of 0.017 mm for polyether, 0.023 mm for medium-viscosity addition silicone, 0.036 mm for putty-wash addition silicone, and 0.066 mm for reversible hydrocolloid all fall within the limits of accuracy as determined by experienced clinicians. When assembled units were evaluated, the mean marginal discrepancy for elastomeric impression materials changed little from that of the individual units, whereas the reversible hydrocolloid impressions exhibited a more significant change. The technique of our investigation may have affected the results. The thickness of all of the impression materials was controlled by the use of a standardized relief in the custom trays for the elastomerics and by a palatal stop for the reversible hydrocolloid. The common use of the elastomerics in a clinical situation is with a stock tray. It is conceivable that by controlling the thickness of the elastomerics the accuracy was enhanced. For making the reversible hydrocolloid impression, the master model was warmed to 98” F as suggested by the manufacturer, and when the castings were fitted to the master model it was done at room temperature. If the 25’ to 30° F difference in, temperature resulted in a slight dimensional change of the plastic master model, it might have had a negative impact on the reversible hydrocolloid material.
168
DOUNIS
Table V. Multiple range test for mean marginal opening for each group luted on dentoform
Group Group
AND
Mean
(w)
1
2
3
'4
29.4 23.0 40.2
NS NS
NS NS
NS NS -
* * *
116.1
*
*
*
-
Kay same as in Table IV.
By changing the protocol of this investigation to simulate the clinical situation, we were able to report data that are more clinically relevant. In the studies by StauRer et al.‘” and Lin et a1.i7a single casting was made for each abutment on the master model and subsequently assembled on the master model to produce a master full-arch restoration. The master FPD, in turn, was placed on casts made from the various impression materials to compare their accuracy. This procedure resulted in vertical marginal openings that were quite large and thus raised questions regarding the clinical relevance of the data. The design of our experiment required that individual castings be made for each abutment on the die stone casts made from each impression material, a total of 96 castings. Twenty-four complete-arch FPDs were assembled on their respective casts and then placed on the master model to determine their accuracy. Although a change from previous studies on the relative accuracy of the materials was not demonstrated, the data gathered on the marginal integrity of the units were more clinically relevant. For example, the study by Lin et all7 reported marginal openings of the assembled units for reversible hydrocolloid of more than 0.500 mm, but in the present study the mean marginal opening was 0.119 mm. It would seem that simulating the clinical situation was more appropriate.
SUMMARY The accuracy of four impression materials commonly used for a complete-arch fixed partial denture was compared. The materials were polyether, medium-viscosity and putty-wash addition silicones, and reversible hydrocolloid. Ninety-six abutment crowns were made on stone casts constructed from impressions of a maxillary complete-arch dentoform having four abutment full-crown preparations with shoulder margins. The abutment crowns were luted together with Duralay resin by use of a special metal frame to produce 24 complete-arch restorations. The vertical marginal openings of the retainers were measured on the dentoform as single restorations and as complete arch restorations.
CONCLUSIONS Under the conditions of this study, the following conclusions were drawn.
FEBRUARY
1991
VOLUME
65
NUMBER
2
IMPRESSION
MATERIALS
FOR COMPLETE-ARCH
FPDs
1. The polyether and addition-silicone impression materials were significantly more accurate than the reversible hydrocolloid impression material in producing dies for single restorations. However, all of the impression materials tested produced clinically acceptable single crowns. 2. The polyether and addition-silicone impression materials produced accurate casts that would enable the fabrication and assembly of clinically acceptable FPDs. 3. Reversible hydrocolloid impression material produced casts that were not sufficiently accurate to allow for the assembly of clinically acceptable complete arch FPDs.
8. Sawyer HF, Birtles JT, Neiman R, Podshadley AG. Accuracy of casts
produced from seven rubber impression materials. J Am Dent Assoc 1973;87:126-30. 9. Sawyer HF, Dilts WE, Aubrey ME, Neiman R. Accuracy of casts produced from the three classes of elastomer impression materials. J Am Dent Assoc 1974;89:644-8. 10. Vermilyea SG, Powers JM, Craig RG. Polyether, polysulfide and silicone rubber impression materials: part 2: accuracy of silver-plated dies. J Mich Dent Assoc 1975;57:405-10. 11. Stackhouse JA. A comparison of elastic impression materials. J PROSTHET DENT 1975;34:305-13. 12. Munoz C, Goodacre C, Schnell R, Harris R. Laboratory and clinical
study of a visible light polymerized elastomeric impression material. Int J Proathodont
1988;1:59-66. 13. Henry PJ, Harnist DJR. Dimensional stability and accuracy of rubber
impression materials. Aust Dent J 1974;19:162-6.
REFERENCES
14. Lacy AM, Fukui H, Bellman T, Jendresen MD. Time-dependent accu-
1. Brindsden GI, Sorensen S, McClenahan J. Dimensional accuracy of five
impression materials using a copper-shell technique. J Dent Res 1964;43 (Suppl):911. 2. Hembree JH Jr. Comparative accuracy of elastomer impression materials. J Term Dent Assoc 1974;54:164-7. 3. Eames WB, Wallace SW, Suway NB, Rogers LB. Accuracy and dimensional stability of elastomeric impression materials. J PROSTHET DENT 1979;42:159-62. 4. Ciesco JN, Malone WFP, Sandrik JL, Maxur B. Comparison of elasto-
meric impression materials used in fixed prosthodontics. J PROSTH~ DENT 1981;45:89-94. 5. Mincham W, Thurgate SM, Lewis AJ. Measurement of dimensional
stability of elastomeric impression materials by holographic interferometry. Aust Dent J 1981;26:395-9. 6. Tjan AHL, Whang S, Tjan AH, Sarkissian R. Clinically oriented evaluation of the accuracy of commonly used impression materials. J PROSTHET DENT 1986;56:4-8.
7. Bassett RW, Vander Heide JD, Smith DD. Clinically oriented tests comparing accuracy of elastic impression materials. J South Calif Dent Assoc 1969;37:47-57.
A qualitative Part II
racy of elastomer impression materials, part II: polyethers, polysulfides, and polyvinylsiloxanes. J PROSTHET DENT 1981;45:329-33. 15. Linke B, Nicholls J, Faucher R. Distortion analysis of stone casts made from impression materials. J PROSTHET DENT 1985;54:794-802. 16. Stauffer J, Meyer J, Nally J. Accuracy of six elastic impression materials used for complete-arch fixed partial dentures. J PROSTHET DENT 1976;35:407-15. 17. Lin CC, Ziebert G, Donegan SJ, Dhuru V. Accuracy of impression materials for complete arch fixed partial dentures. J PROSTHET DENT 1988;59:288-91. 18. Christensen G. Marginal fit of gold inlay castings. J PROSTHET DENT 1966;16:297-305. 19. Dedmon H. Disparity in expert opinions on size of acceptable marginal
openings. J Oper Dent 1982;7:97-101. Reprint requests to: DR. GERALD J. ZIFBERT SCHOOL OF DENTISTRY MARQUEITE UNIVERSITY 604 N. 16TH ST. MILWAUKEE, WI 53233
study for the bond and color of ceramometals.
Ihab Adel Hammad, B.D.S., M.S., D.Sc.,* and Robert Sheldon Stein, D.M.D.** Boston University, School of Graduate Dentistry, Boston, Mass. Many dentists, porcelain manufacturers, and dental technicians empirically state that repeated firings tend to bleach out or alter the original shade of porcelain. This investigation used a sophisticated calorimeter to resolve the controversy. The effect of temperature rise and number of firings had varying effects on color relative to brand of porcelain and specific alloy. (J PROSTHET DENT 1991;&169-79.)
T
he dental profession has long been confronted with the problem of matching the color of artificial tooth substances to the natural dentition. The selection or mod*Former graduate student, Department of Prosthodontics. **Research Professor, Department of Prosthodontics, and Assistant Dean for Clinical Affairs. 10/l/14563
THE JOURNAL
OF PROSTHETIC
DENTISTRY
ification of color for a ceramic restoration is complex and requires careful consideration. Selection of the proper color (shade) is dependent upon the ability of the dental ceramist to analyze the nuances found in natural teeth and to recognize the need for subsequent modifications. Modifications are possible since color is a three-dimensional phenomenon. A ceramic restoration or a tab from a shade guide, when compared with a tooth, may appear to be more
169
materials
Georgia S. Dounis, D.D.S.,* Gerald J. Ziebert, Kiki S. Dounis, D.D.S.*
for complete-arch
fixed
D.D.S., M.S.,** and
Marquette University, School of Dentistry, Milwaukee, Wis. This study compared the marginal fit of complete-arch fixed prostheses under simulated clinical conditions. Prostheses were made on casts constructed from three commonly used impression materials; polyether, polyvinyl siloxane (mediumviscosity and putty-wash), and reversible hydrocolloid. A maxillary dentoform with four abutment teeth was used as the master cast and six impressions were made with each material. Individual castings for each abutment were made on the stone casts. The abutment castings were luted together on the casts to provide a complete-arch fixed partial denture using a ticonium framework and acrylic resin. The marginal fit of the abutment castings was measured on the master cast before and after the prostheses were luted together. The polyether and both addition silicone impression materials were significantly more accurate than the reversible hydrocolloid in both situations. All of the single castings were clinically acceptable, but the luted restorations made from reversible hydrocolloids were not. (J PROSTHET DENT 1991;65:165-9.)
D.
lmensional accuracy of impression materials is crucial for the production of working casts in fixed prosthodontics. Accurate replications of tooth preparations
and their arch positions require impression materials that exhibit limited distortion. Research on dimensional
stability
of impression
materi-
als commonly has concentrated on the accuracy of individual dies1-6 and quadrant fixed partial denture (FPD) abutments.7-12 Few studies have reported the accuracy of complete-arch
impressions.
Henry
and Harnist13
com-
pared the accuracy of 14 different impression materials by using a four-posted, silver-plated, full-arch model. They concluded that polyethers were the most reliable. A study of full-arch impressions of two machined aluminum alloy dies14found addition-silicones the most stable, followed by polyethers. Another study,15 using a full-arch metal model, compared impression materials by measuring faciolingual and mesiodistal widths and the height of the stone casts versus the master model. Reversible hydrocolloid produced less interabutment distortion. The accuracy of six impression materials, used in complete-arch FPD impressions with four intricate abutment preparations machined of
stainless steel was investigated,16 and a similar study used complete crown preparations on a dentoform (Columbia Dentoform Corp., New York, N.Y.) model to compare the accuracy of six impression materials.‘? In both studies, a prosthesis was made on the master model and adaptation was evaluated on casts obtained from the various impression materials. Both concluded that polyethers, followed by addition silicones, produced the most accurate working casts. Neither reflected the procedure normally followed in restorative therapy. In clinical situations, restorations are made on working casts and then placed in the mouth. Our experiments used castings that were made and assembled on the working cast and then placed on the master model, to determine the accuracy of four commonly used impression materials. METHODS
AND
MATERIAL
Three impression materials were used in this study: polyether (Impregum F, Premier, ESPE, West Germany); addition silicone (Mirror 3 medium-viscosity, single-mix, and Mirror 3 putty-wash, Sybron/Kerr, Romulus, Mich.); and reversible hydrocolloid (Acculoid, Van R, Los Angeles, Calif.).
Presented at the Academy of Denture Prosthetics meeting, Corpus Christi, Tex. *Graduate student, Department of Prosthodontics. **Professor and Chairman, Department of Prosthodontics. 10/l/21771
THE
JOURNAL
OF
PROSTHETIC
DENTISTRY
Six satisfactory impressions were obtained for each of the materials for a total of 24 impressions. A maxillary partially edentulous model (Model No. 567M, Columbia Dentoform Corp.) was modified as the master model. The first premolars were removed and the sockets were filled with inlay pattern resin (Duralay, Reliance Dental Mfg. Co., Worth, Ill.). The remaining canines (teeth No. 6 and
165
DOUNIS,
ZIEBERT.
AND
DOUNIS
Fig. 1. Modified dentoform model with abutment preparations used as master model. Fig. 2. Ticonium framework used to lute FPD. Fig. 3. Measuring sites for each abutment. MB, Mesiobuccal measuring position; B, buccal measuring position; DB, distobuccal measuring position. Fig. 4. FPD luted together with ticonium framework by Duralay resin.
11) and second molars (teeth No. 2 and 15) were the four abutment teeth for the maxillary prosthesis. The root surfaces of the abutment teeth and their respective sockets were roughened and scored. The sockets were filled with DuraIay resin, the teeth were immediately replaced, and the screws were tightened to secure each abutment to the base. After 48 hours the abutment teeth were prepared for complete crowns with 1 mm shoulder margins by use of a handpiece mounted on a parallelometer (Fig. 1). A handle was mounted on the base of the dentoform to enhance separation of the impressions from the models in a straight line to minimize distortion. For the polyether and addition-silicone impressions, custom acrylic resin trays were constructed with a 4 mm uniform space. Metal rimlocked water-cooled trays were used for the reversible hydrocolloid impressions. An acrylic resin stop was placed in the palatal region of the rim-locked tray to provide a minimum of 2 mm of space over the occlusal surfaces of the abutments. The setting time for the polyether and addi-
166
tion-silicone materials was doubled to compensate for polymerization at room temperature. For the reversible hydrocolloid impressions, the dentoform was tempered at 98” F for 10 minutes before the impressions were made. The temperature of the water circulating through the tray had a range of 65’ to 72’ F and the impression was allowed to gel for 8 minutes. All of the impressions were manually held in place throughout the setting period. The impressions were immediately poured in a vacuum-mixed die stone (Die Keen, Columbus Dental Mfg., St. Louis, MO.), except the addition silicones, which were poured after 20 minutes. The casts of the reversible hydrocolloid impressions were placed in a humidor while setting. The casts were separated after 1 hour, trimmed after 2 hours, and examined under X10 magnification to remove minor bubbles with a sharp instrument. Individual ceramometal cast copings (Olympia, J. F. Jelenko & Co., Armonk, N.Y.) were made for each of the abutment dies on the 24 casts for a total of 96 castings. The flat occlusal surface of each coping was roughened to facil-
FEBRUARY
1991
VOLUME
65
NUMBER
2
IMPRESSION
MATERIALS
FOR
COMPLETE-ARCH
FPDs
I. Mean marginal openings of individual castings at each abutment (in pm)
Table
Table II. Mean marginal openings of assembled castings at each abutment (in km) Abutment
Abutment
Type of impression
Right second molar --f
Left second molar
Left canine
Right canine
SD
Ti
SD
si
SD
ii
SD
x
-
Right canine
SD
iI
Left canine
Left second molar
Tt
iii
-
SD
SD
SD
1
10
8
19
8
34
10
7
5
1
38
13
36
9
24
8
20
2
41
18
17
7
29
12
6
5
2
40
14
8
5
34
11
10
9
3
41
11
34
10
43
15
28
9
3
54
11
25
9
21
8
60
14
4
37
15
66
6
120
20
28
10
4
75
18
125
16
123
21
141
29
Materials: 1, Polyether; 2, vinyl polysiloxane (medium polysiloxane (putty/wash); 4, Reversible hydrocolloid.
viscosity);
3, vinyl
itate attachment of a cast ticonium framework used to lute the copings together (Fig. 2). The castings were examined under X10 magnification, small bubbles and irregularities were removed, and the copings were fitted to their respective dies. Each cast was mounted on a surveyor table. The individual castings were seated with light finger pressure and the vertical marginal discrepancy was measured with a travelling microscope graduated in 0.001 mm. Three sites were measured: the mesiofacial (MF), midfacial (F), and distofacial (DF) aspect of each casting for Nos. 2,6,11, and 15. The same measuring procedure was followed after the copings were placed on the Dentoform model (Fig. 3). The copings were returned to the stone casts and luted together by use of inlay resin (Duralay) and the ticonium framework (Fig. 4). The luting procedure was completed one joint at a time, with a lo-minute setting time allowed before proceeding to the next joint. The marginal openings were again measured at the three sites of each abutment. The one-piece unit was then removed from the stone dies, seated on the dentoform with light finger pressure, and the vertical marginal discrepancies were again measured at the designated sites.
RESULTS The mean marginal openings for all of the castings on the working casts were less than 0.025 mm. Table I shows the mean marginal opening of the individual castings at each abutment on the dentoform. Table II shows the mean marginal opening of the castings on the dentoform after they had been luted on the working cast and transferred to the dentoform. To assess the difference among the materials, a one-way analysis of variance was performed of material on the cast, on the dentoform, luted on the cast, and on the dentoform after the specimen was luted on the cast. The analysis of the unassembled castings on the dentoform revealed significant differences (p < 0.05) among the materials. The analysis also disclosed significant differ-
THE
-
Type of impression
Right second molar
JOURNAL
OF PROSTHETIC
DENTISTRY
Material: 1, Polyether; 2, vinyl polysiloxane (medium polysiloxane (putty/wash); 4, Reversible hydrocolloid.
Table
III.
viscosity);
8
3, vinyl
Summary of analyses of variance
Source of variation
DF
SS
3
MS
F-Ratio
p
14.0079
0.05). *Significant @ < 0.05).
DISCUSSION Consistent with previous reports,61iis 16*l7 this study demonstrated that polyether impressions were the most accurate. The addition silicones were a close second and not inferior when judged statistically. The reversible hydrocolloids were the least accurate of the four forms of materials, showing statistically significant differences from the rest. This difference held true whether the castings were fitted to the master model individually or luted to create a complete-arch restoration. With the range of clinically acceptable open margins as reported by Christensen18 (0.034 mm to 0.119 mm with a mean of 0.074 mm) and by Dedmonlg (mean of 0.114 mm), it is evident that the unassembled units made from all four forms of impression materials would be clinically acceptable. Mean vertical marginal discrepancies of 0.017 mm for polyether, 0.023 mm for medium-viscosity addition silicone, 0.036 mm for putty-wash addition silicone, and 0.066 mm for reversible hydrocolloid all fall within the limits of accuracy as determined by experienced clinicians. When assembled units were evaluated, the mean marginal discrepancy for elastomeric impression materials changed little from that of the individual units, whereas the reversible hydrocolloid impressions exhibited a more significant change. The technique of our investigation may have affected the results. The thickness of all of the impression materials was controlled by the use of a standardized relief in the custom trays for the elastomerics and by a palatal stop for the reversible hydrocolloid. The common use of the elastomerics in a clinical situation is with a stock tray. It is conceivable that by controlling the thickness of the elastomerics the accuracy was enhanced. For making the reversible hydrocolloid impression, the master model was warmed to 98” F as suggested by the manufacturer, and when the castings were fitted to the master model it was done at room temperature. If the 25’ to 30° F difference in, temperature resulted in a slight dimensional change of the plastic master model, it might have had a negative impact on the reversible hydrocolloid material.
168
DOUNIS
Table V. Multiple range test for mean marginal opening for each group luted on dentoform
Group Group
AND
Mean
(w)
1
2
3
'4
29.4 23.0 40.2
NS NS
NS NS
NS NS -
* * *
116.1
*
*
*
-
Kay same as in Table IV.
By changing the protocol of this investigation to simulate the clinical situation, we were able to report data that are more clinically relevant. In the studies by StauRer et al.‘” and Lin et a1.i7a single casting was made for each abutment on the master model and subsequently assembled on the master model to produce a master full-arch restoration. The master FPD, in turn, was placed on casts made from the various impression materials to compare their accuracy. This procedure resulted in vertical marginal openings that were quite large and thus raised questions regarding the clinical relevance of the data. The design of our experiment required that individual castings be made for each abutment on the die stone casts made from each impression material, a total of 96 castings. Twenty-four complete-arch FPDs were assembled on their respective casts and then placed on the master model to determine their accuracy. Although a change from previous studies on the relative accuracy of the materials was not demonstrated, the data gathered on the marginal integrity of the units were more clinically relevant. For example, the study by Lin et all7 reported marginal openings of the assembled units for reversible hydrocolloid of more than 0.500 mm, but in the present study the mean marginal opening was 0.119 mm. It would seem that simulating the clinical situation was more appropriate.
SUMMARY The accuracy of four impression materials commonly used for a complete-arch fixed partial denture was compared. The materials were polyether, medium-viscosity and putty-wash addition silicones, and reversible hydrocolloid. Ninety-six abutment crowns were made on stone casts constructed from impressions of a maxillary complete-arch dentoform having four abutment full-crown preparations with shoulder margins. The abutment crowns were luted together with Duralay resin by use of a special metal frame to produce 24 complete-arch restorations. The vertical marginal openings of the retainers were measured on the dentoform as single restorations and as complete arch restorations.
CONCLUSIONS Under the conditions of this study, the following conclusions were drawn.
FEBRUARY
1991
VOLUME
65
NUMBER
2
IMPRESSION
MATERIALS
FOR COMPLETE-ARCH
FPDs
1. The polyether and addition-silicone impression materials were significantly more accurate than the reversible hydrocolloid impression material in producing dies for single restorations. However, all of the impression materials tested produced clinically acceptable single crowns. 2. The polyether and addition-silicone impression materials produced accurate casts that would enable the fabrication and assembly of clinically acceptable FPDs. 3. Reversible hydrocolloid impression material produced casts that were not sufficiently accurate to allow for the assembly of clinically acceptable complete arch FPDs.
8. Sawyer HF, Birtles JT, Neiman R, Podshadley AG. Accuracy of casts
produced from seven rubber impression materials. J Am Dent Assoc 1973;87:126-30. 9. Sawyer HF, Dilts WE, Aubrey ME, Neiman R. Accuracy of casts produced from the three classes of elastomer impression materials. J Am Dent Assoc 1974;89:644-8. 10. Vermilyea SG, Powers JM, Craig RG. Polyether, polysulfide and silicone rubber impression materials: part 2: accuracy of silver-plated dies. J Mich Dent Assoc 1975;57:405-10. 11. Stackhouse JA. A comparison of elastic impression materials. J PROSTHET DENT 1975;34:305-13. 12. Munoz C, Goodacre C, Schnell R, Harris R. Laboratory and clinical
study of a visible light polymerized elastomeric impression material. Int J Proathodont
1988;1:59-66. 13. Henry PJ, Harnist DJR. Dimensional stability and accuracy of rubber
impression materials. Aust Dent J 1974;19:162-6.
REFERENCES
14. Lacy AM, Fukui H, Bellman T, Jendresen MD. Time-dependent accu-
1. Brindsden GI, Sorensen S, McClenahan J. Dimensional accuracy of five
impression materials using a copper-shell technique. J Dent Res 1964;43 (Suppl):911. 2. Hembree JH Jr. Comparative accuracy of elastomer impression materials. J Term Dent Assoc 1974;54:164-7. 3. Eames WB, Wallace SW, Suway NB, Rogers LB. Accuracy and dimensional stability of elastomeric impression materials. J PROSTHET DENT 1979;42:159-62. 4. Ciesco JN, Malone WFP, Sandrik JL, Maxur B. Comparison of elasto-
meric impression materials used in fixed prosthodontics. J PROSTH~ DENT 1981;45:89-94. 5. Mincham W, Thurgate SM, Lewis AJ. Measurement of dimensional
stability of elastomeric impression materials by holographic interferometry. Aust Dent J 1981;26:395-9. 6. Tjan AHL, Whang S, Tjan AH, Sarkissian R. Clinically oriented evaluation of the accuracy of commonly used impression materials. J PROSTHET DENT 1986;56:4-8.
7. Bassett RW, Vander Heide JD, Smith DD. Clinically oriented tests comparing accuracy of elastic impression materials. J South Calif Dent Assoc 1969;37:47-57.
A qualitative Part II
racy of elastomer impression materials, part II: polyethers, polysulfides, and polyvinylsiloxanes. J PROSTHET DENT 1981;45:329-33. 15. Linke B, Nicholls J, Faucher R. Distortion analysis of stone casts made from impression materials. J PROSTHET DENT 1985;54:794-802. 16. Stauffer J, Meyer J, Nally J. Accuracy of six elastic impression materials used for complete-arch fixed partial dentures. J PROSTHET DENT 1976;35:407-15. 17. Lin CC, Ziebert G, Donegan SJ, Dhuru V. Accuracy of impression materials for complete arch fixed partial dentures. J PROSTHET DENT 1988;59:288-91. 18. Christensen G. Marginal fit of gold inlay castings. J PROSTHET DENT 1966;16:297-305. 19. Dedmon H. Disparity in expert opinions on size of acceptable marginal
openings. J Oper Dent 1982;7:97-101. Reprint requests to: DR. GERALD J. ZIFBERT SCHOOL OF DENTISTRY MARQUEITE UNIVERSITY 604 N. 16TH ST. MILWAUKEE, WI 53233
study for the bond and color of ceramometals.
Ihab Adel Hammad, B.D.S., M.S., D.Sc.,* and Robert Sheldon Stein, D.M.D.** Boston University, School of Graduate Dentistry, Boston, Mass. Many dentists, porcelain manufacturers, and dental technicians empirically state that repeated firings tend to bleach out or alter the original shade of porcelain. This investigation used a sophisticated calorimeter to resolve the controversy. The effect of temperature rise and number of firings had varying effects on color relative to brand of porcelain and specific alloy. (J PROSTHET DENT 1991;&169-79.)
T
he dental profession has long been confronted with the problem of matching the color of artificial tooth substances to the natural dentition. The selection or mod*Former graduate student, Department of Prosthodontics. **Research Professor, Department of Prosthodontics, and Assistant Dean for Clinical Affairs. 10/l/14563
THE JOURNAL
OF PROSTHETIC
DENTISTRY
ification of color for a ceramic restoration is complex and requires careful consideration. Selection of the proper color (shade) is dependent upon the ability of the dental ceramist to analyze the nuances found in natural teeth and to recognize the need for subsequent modifications. Modifications are possible since color is a three-dimensional phenomenon. A ceramic restoration or a tab from a shade guide, when compared with a tooth, may appear to be more
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